AbstractThe Asian kelp Undaria pinnatifida was first reported in north-western Spain in 1988. Since then, it has spread along the Galician coasts and towards the western Cantrabrian coast, probably supported by new introductions related to aquaculture and private yachts. Despite the high potential of this seaweed to invade new areas, it has not fully established itself in specific areas along the eastern Cantabrian coast where it has been farmed. We attempted to identify the macro-environmental determinants for the successful establishment of U. pinnatifida in the northern Iberian coast. Thus, we built a model based on the significant relationships between this kelp and several environmental factors using the Favourability Function, a method based on binary logistic regression. We obtained a statistically significant Favourability model where the chlorophyll concentration in summer was the most influential variable and the photosynthetically active radiation in spring was a secondary variable that best characterized the presence of U. pinnatifida. The ecological implications are discussed.